The problem is, most leaders are best trained to be one. Just because you get promoted to a higher position doesn't mean you'll know how to manage people immediately.
This is why all companies should provide leadership trainings to all employees with higher positions but alas. Most people are unaware that they need training for higher positions in order to be a competent leader.
My employer, at least offers leadership training to management personnel, but I don't know if they require it. They require training for team leaders and supervisors before those positions are granted; plus, candidates have to have good recommendation from their supervisors.
Oh this also applies to government officials.